In several examples it may be unnecessary to remove a second substrate layer 310 to create the intermediate waveguide structure 400. For instance, a second substrate 310 may not be bonded or applied to the spacer layer 215. In this example, only a second waveguide layer 305 is applied to the spacer layer 215. In another example, a second waveguide layer 305 may be grown on the spacer layer 215 through any reasonably suitable chemical vapor deposition process described above, thus rendering removal of a second substrate layer unnecessary.
FIG. 7 illustrates a slot waveguide structure 700, according to another embodiment. The waveguide structure 700 may include the substrate 110, the waveguide layer 105 forming a rail, the spacer layer 215 forming a slot, and the waveguide layer 305 forming a rail. Portions of the waveguide layer 305 forming a rail may be selectively removed in any reasonably suitable configuration to form apertures 705. The removal of portions to create apertures 705 may also extend through the spacer layer 215 forming the slot, and through the waveguide layer 105 forming the rail. The apertures 705 may form microcavities, such as a photonic crystal cavity.